You can use plunger first to pull off what caused the clogging. If the drain still remains blocked try to pour half a cup of baking soda down the drain. Afterwards, pour about three cups of boiling water. The baking soda and the hot water cause a reaction that may dissolve and move through the clog.

Many times, side by side lavatory sinks and back to back lavatory sinks are plumbed into their vent stack using what is commonly known as a "cross" fitting. If you try to run a cable through one sink, many times, the cable will go straight through the cross and end up in the trap of the other sink. What you have to do is find the vent stack in the wall above the flood rim level of the sinks - this means above the countertop level. I usually go about a foot above - drill a 1/2" diameter hole in the pipe so you can get your 1/4" cable down the vent stack. That is, unless you can gain access to vent easily from the roof or attic, where you don't have to damage your walls. I hope this helps. Friendly Home Services Baton Rouge...

Many times, side by side lavatory sinks and back to back lavatory sinks are plumbed into their vent stack using what is commonly known as a "cross" fitting. If you try to run a cable through one sink, many times, the cable will go straight through the cross and end up in the trap of the other sink. What you have to do is find the vent stack in the wall above the flood rim level of the sinks - this means above the countertop level. I usually go about a foot above - drill a 1/2" diameter hole in the pipe so you can get your 1/4" cable down the vent stack. That is, unless you can gain access to vent easily from the roof or attic, where you don't have to damage your walls. I hope this helps. Friendly Home Services Baton Rouge...

You drill a hole in the pipe!!! Then you snake a 1-1/2 drain with a 1/4" cable? The first obstruction you hit the cable will turn on it self and may become stuck in the line. This is some of the worst advice I have seen on this site. What do you do with the hole in the pipe put chewing gum in it?

Photos of the last time I used this technique are found by searching dinoseer or FriendlyHomeServices on Flicker dot com - I don't have enough posts yet to allow links...

Yes, ultimately to be to "code", one would ideally cut a Tap Tee to serve as a clean out for future stoppages. If you have a PVC or ABS Vent Stack, you could just cut the stack above the flood rim and put the pipe back together with a no-hub or fernco coupling.

I am a Master Plumber with nearly 30 years experience - I have used this technique many, many times on fixtures plumbed with a cross or in the case of the Drain in my above referenced pictures, my cable kept going up the Vent Stack due to the stoppage being right below where the Lavatory Drain Arm entered a Tap Tee on the Vent Stack.

I also use a high quality American Made 1/4" solidcore cable on my Rigid Drain Machine. I can unstop anything up to a Main Sewer Line...

You drill a hole in the pipe!!! Then you snake a 1-1/2 drain with a 1/4" cable? The first obstruction you hit the cable will turn on it self and may become stuck in the line. This is some of the worst advice I have seen on this site. What do you do with the hole in the pipe put chewing gum in it?

John

Even though the original poster is probabbly long gone.
I have to agree with John on this for another reason. Cutting into and snaking a vent to to clear what is probably a clogged trap seems extreme and not likely to work. What ever happened to trying liquid plumber or some other drain cleaner or removing the trap first. With a bunch of girls in the house, I've cleaned hair out of many a trap. Nowdays I try the drain cleaner first.